1. Field of the Invention
The present invention relates to multiplexing devices and processes generally, and more particularly, to a device and process for multiplexing cells by dynamically controlling a buffer.
2. Description of the Related Art
In general, a multiplexing device sequentially selects and transmits input data. A Round Robin multiplexing system is configured to sequentially transmit the data (cell) received in buffers that are provided at each input port. Typically, a multiplexing device sequentially reads the data received to each of the buffers. The Round Robin system reads and transmits the data (cell) stored in a corresponding buffer while making an orderly selection of each of the buffers. I have found however, with multiplexers using a Round-Robin system, that the cell can be lost due to buffer overflow or that buffer delay can occur when traffic concentrates on a particular buffer.
The traffic concentration at a particular buffer during multiplexing as above occurs as follows. First concentration of traffic can occur when the traffic originates due to burstiness of the source. Second, during the internal for the routing process in the network, the concentration of traffic occurs when a plurality of incoming traffic is received for the same point of destination. Third, the traffic concentrates when the burstiness increases in the traffic due to jitter occurring due to diverse delays inside the net. Accordingly, in multiplexing devices using the Round Robin system, when the input traffic is not uniform and the burstiness becomes strong, the number of the cells being received at a particular cell will correspondingly increase. Thus, cell loss can occur due to buffer overflow if attributable to the concentration of the traffic; also, cell transmission delay can occur inside the buffer. I have observed that since the use efficiency of the buffer deteriorates substantially in the event that the number of the cells received by a particular buffer is substantially reduced, multiplexing devices using the Round Robin system are not effective when the traffic is not uniform and when the destination of the traffic tends to be concentrated.
Earlier efforts in asynchronous transmission mode cell switching, such as the Supervision Control System of Yoshimura et al., U.S. Pat. No. 5,394,396, and the Arrangement For Controlling Shared-buffer-memory Overflow In A Multi-priority Environment of Pashan, et al., U.S. Pat. No. 5,233,606, depended upon circuits that not infrequently discarded cells. Other efforts such as the Method And A System Of Control Of Asynchronous Time Communication Outputs of Boyer, et al., U.S. Pat. No. 5,299,191, depended upon continuous comparisons of buffer occupancy in time division multiplexing.
Designs such as the Output-Buffer Switch For Aschronous Transfer Mode of Kenji Yamada, U.S. Pat. No. 5,455,820, endeavored to avoid loss of cells by operating a buffer controller on the basis of a determination of occupancy ratio relative to a predetermined threshold. These designs however, seem to require an excessive number of buffers, and incur concomitant delay in transmission of the multiplexed cells.
More recent efforts in the art, such as the Asynchronous Transfer Mode (ATM) Multiplexing Process Device And Method Of The Broadband Integrated Service Digital Network Subscriber Access Apparatus, by Seung W. Shon, U.S. Pat. No. 5,499,238, for example have sought to use a complex ranking of cells using determinations of whether a buffer is full and the class order of each of the cells. Efforts to address the problems attendant to non-uniform traffic and undue concentration can not be reliably addressed however, on a classification scheme that depends in part upon the occurrence of full buffers.